The guy who said online IQ tests are bullshit is right, with the exception of a few of them. Most of them are more like a collection of random riddles, rather than actually having varying difficulties and testing your brainpower.
http://www.iqtest.dk/main.swf is an example of a pretty good test. It's based upon Raven's progressive matrices, so is culture fair too, and is based on the answers of 250 000 people.
Also, after actually sending this test to a few people, the answers seem to be more accurate. People I know who get 80s UAIs seemed to get between 110 and 120, which makes sense coz those 2 values cut off about 75% of the pop (110) and 91% of the pop (120).
Of course, it won't compare to a test by a professional psychologist, but it's probably the best you'll find online.
BTW it's capped at 145 I think.